Method of fabricating high-voltage MOS device

ABSTRACT

A HV-MOS device is described, including a substrate, a gate dielectric layer and a gate, a channel region, two doped regions as a source and a drain, a field isolation layer between the gate and at least one of the two doped regions, a drift region and a modifying doped region. The drift region is located in the substrate under the field isolation layer and connects with the channel region and the at least one doped region. The modifying doped region is at the periphery of the at least one doped region.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of a prior application Ser. No. 10/709,924, filed Jun. 7, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method for fabricating the same. More particularly, the present invention relates to a high-voltage metal-oxide-semiconductor (HV-MOS) device and a method for fabricating the same.

2. Description of the Related Art

HV-MOS devices are widely used in power circuits, having particular structures for sustaining high voltages and increasing breakdown voltages. FIG. 1 illustrates the top view of a conventional HV-MOS device, which includes a field oxide (FOX) layer 110, a gate 120, a channel region 130 under the gate 120 surrounded by the FOX layer 110, a source region 140 and a drain region 150 beside the channel region 130 each surrounded by the FOX layer 110, and a drift region 160 between the channel region 130 and each of the source region 140 and the drain region 150. The drift region 160 is formed by implanting a dopant into the substrate using a mask layer having an opening 180 therein as one part of the implantation mask. Before the implantation, the regions predetermined for the channel region 130, the source region 140 and the drain region 150 are covered with another mask layer that defines the active areas and serves as the other part of the implantation mask.

In the above-mentioned HV-MOS device, the FOX layer 110 between the channel region 130 and the source/drain region 140/150 serves as a field isolation layer that allows the device to sustain a high voltage. In addition, the source/drain region 140/150 usually consists of a heavily doped contact region and a lightly doped grade region under the contact region for increasing the breakdown voltage of the device. However, breakdown still occurs easily at the corners of the grade regions.

SUMMARY OF THE INVENTION

In view of the foregoing, this invention provides a high-voltage metal-oxide-semiconductor (HV-MOS) device that has a higher breakdown voltage.

This invention also provides a method for fabricating a HV-MOS device capable of increasing the breakdown voltage of the HV-MOS device.

The HV-MOS device of this invention includes a substrate, a gate dielectric layer, a gate, a channel region, two doped regions as a source and a drain, a field isolation layer, a drift region and a modifying doped region. The gate dielectric layer is disposed on the substrate, the gate on the gate dielectric layer, and the channel region in the substrate under the gate dielectric layer. The two doped regions as the source and the drain are located in the substrate beside the gate, and the field isolation layer between the gate and at least one of the two doped regions. The drift region is located in the substrate under the field isolation layer and connects with the channel region and the at least one doped region, and the modifying doped region in the substrate at the periphery of the at least one doped region.

In the method for fabricating a HV-MOS device of this invention, the regions of the substrate where the channel region, the source and the drain region will be formed are firstly covered with a mask layer. A portion of the substrate between the channel region and the region predetermined for the at least one doped region and another portion of the substrate at the periphery of the predetermined region are implanted with a dopant to form doped regions. A field isolation layer is then formed on the exposed portions of the substrate, while the doped region under the field isolation layer between the channel region and the predetermined region serves as a drift region, and the doped region under the field isolation layer at the periphery of the predetermined region serves as a modifying doped region. Thereafter, a gate dielectric layer and a gate are formed covering the channel region, and a source region and a drain region are formed in the substrate beside the gate using the gate and the field isolation layer as a mask.

In the HV-MOS device of this invention, the modifying doped region at the periphery of the at least one doped region separated from the gate by the field isolation layer can increase the breakdown voltage of the device. It is more preferable that the modifying doped region and the drift region together completely surround the at least one doped region for effectively increasing the breakdown voltage.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 illustrates the top view of a conventional HV-MOS device.

FIGS. 2A and 2B illustrate a HV-MOS device according to a preferred embodiment of this invention in a top view and in a cross-sectional view along line II–II′, respectively.

FIGS. 3, 4 and 2A/2B illustrate a process flow of fabricating a HV-MOS device according to the preferred embodiment of this invention, wherein FIGS. 3 and 4 are also cross-sectional views along line II–II′.

FIG. 5 shows the test result of HV-PMOS and HV-NMOS devices of 80 V or 120 V according to the preferred embodiment of this invention, wherein x-axis represents the width “W” (μm) of the modifying doped region and y-axis the breakdown voltages of the HV-MOS devices.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2A and 2B illustrate a HV-MOS device according to the preferred embodiment of this invention in a top view and in a cross-sectional view along line II–II′, respectively. Referring to FIGS. 2A and 2B, the HV-MOS device includes a substrate 200, a field isolation layer 210 on a substrate 200, a gate 220, a gate dielectric layer 222, a channel region 230, a source region 240 and a drain region 250, two drift regions 260 and two modifying doped regions 270.

The substrate 200 is, for example, a single-crystal silicon wafer, and the field isolation layer 210 may be a field oxide (FOX) layer formed with a thermal oxidation process. The gate dielectric layer 222 is disposed on the substrate and surrounded by the field isolation layer 210, the gate 220 covers the gate dielectric layer 222, and the channel region 230 is located in the substrate 200 under the gate dielectric layer 222 and surrounded by the field isolation layer 210. The source region 240 and the drain region 250 are located in the substrate 210 beside the channel region 230, each being surrounded by the field isolation layer 210. The drift region 260 is located in the substrate 200 under the field isolation layer 210 between the channel region 230 and each of the source region 240 and the drain region 250. In addition, each of the heavily doped source region 240 and drain region 250, i.e., contact regions, further has an underlying grade extension region 262 that is lightly doped.

Referring to FIGS. 2A and 2B again, each modifying doped region 270 is in the substrate 200 at the periphery of the source/drain region 240/250, so that the source/drain region 240/250 is completely surrounded by a drift region 260 and a modifying doped region 270 together. The modifying doped region 270 is for modifying the corner shape of the grade extension region 262, so as to reduce the electric field there and increase the breakdown voltage of the HV-MOS device. In addition, the modifying doped region 270 may have a uniform width (W), as shown in FIG. 2A. The drift regions 260 and the modifying doped regions 270 can be formed simultaneously by implanting a dopant into the substrate 200 using a mask layer having an opening 280 therein as a part of the implantation mask, which is described below in details. The doping concentration of the drift regions 260 and the modifying doped region 270 ranges from 5×10¹⁵/cm³ to 5×10¹⁷/cm³.

FIGS. 3, 4 and 2A/2B illustrate a process flow of fabricating a HV-MOS device according to the preferred embodiment of this invention, wherein FIGS. 3 and 4 are also cross-sectional views along line II–II′. Referring to FIG. 3, a substrate 200 is provided, and then a first mask layer 310 a/b defining the active areas and a second mask layer 320 are sequentially formed on the substrate 200. The first mask layer 310 a/b includes a first part 310 a covering the region of the substrate 200 predetermined for the channel region 230 and two second parts 310 b covering the two regions predetermined for the source region 240 and the drain region 250, respectively. The boundaries of the first part 310 a and the two second parts 310 b of the first mask layer 310 a/b are approximately the same as those of the channel region 230, the source region 240 and the drain region 250, respectively. The first mask layer 310 a/b may include a pad oxide layer and a thick silicon nitride (SiN) layer thereon.

The second mask layer 320 has an opening 280 therein, which exposes the substrate 200 between the first part 310 a and the two second parts 310 b of the first mask layer 310 a/b and another portion of the substrate 200 at the peripheries of the two second parts 310 b. The opening 280 in the second mask layer 320 is preferably formed exposing a portion of the substrate 200 completely surrounding each second part 310 b, so that the drift region 260 and the modifying doped region 270 formed latter together completely surround the grade extension region 262 to effectively increase the breakdown voltage. In addition, the second mask layer 320 may be a patterned photoresist layer. Thereafter, ion implantation 330 is performed to formed doped region 260 and 270 in the substrate 200 using the first mask layer 310 and the second mask layer 320 as an implantation mask. The dosage of the ion implantation 330 ranges from 10¹²/cm² to 10¹⁴/cm²

Referring to FIG. 4, the second mask layer 320 is removed, and then a field isolation layer 210 is formed on the substrate 200 using the first mask layer 310 a/b as a mask. The field isolation layer 210 is preferably formed with a thermal oxidation process, which produces a field oxide (FOX) layer on the exposed portions of the substrate 200, while the dopant in the doped regions 260 and 270 are driven down. The doped regions 260 under the field isolation layer 210 between the first part 310 a and the two second parts 310 b of the first mask layer 310 a/b serve as drift regions, and the doped regions 270 under the field isolation layer 210 at the peripheries of the two second parts 310 b of the first mask layer 310 a/b serve as modifying doper regions.

Referring to FIG. 2A/2B, the first mask layer 310 a/b is removed, and then a gate dielectric layer 222 is formed on the channel region 230. A gate 220 is formed over the substrate 200 covering the gate dielectric layer 222 and the channel region 230 as well as a portion of the field isolation layer 210. A source region 240 and a drain region 250 that are heavily doped to serve as contact regions, as well as the lightly doped grade regions 262, are then formed in the substrate 200 using the field isolation layer 210 and the gate 220 as a mask. The grade regions 262 are formed deeper than the source/drain region 240/250.

FIG. 5 shows the test result of HV-PMOS and HV-NMOS devices of 80 V or 120 V according to the preferred embodiment of this invention, wherein x-axis represents the width “W” of the modifying doped region (FIG. 2A/2B) and y-axis the breakdown voltages of the HV-MOS devices. As shown in FIG. 5, the breakdown voltage of the HV-PMOS or HV-NMOS of 80 V or 120 V can be effectively increased by using the method of this invention.

Since the additional modifying doped region 270 can reduce the corner curvature of the depletion region of the S/D grade region 262, as shown in FIG. 2B, the electric field there can be reduced to increase the breakdown voltage of the HV-MOS devices according to this invention.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 

1. A method for fabricating a high-voltage metal-oxide-semiconductor (HV-MOS) device, comprising: forming a patterned first mask layer on a substrate, having a first part covering a channel region in the substrate and two second parts beside the first part covering two regions of the substrate predetermined for a source and a drain, respectively, wherein the first part is apart from at least one of the two second parts; forming a patterned second mask layer over the substrate, having an opening therein exposing the substrate between the first part and the at least one second part of the first mask layer and exposing another portion of the substrate at periphery of the at least one second part of the first mask layer, wherein at least part of the patterned second mask layer is formed directly on the substrate away from the periphery of the at least one second part of the first mask layer; implanting a dopant into the substrate using the first and second mask layers as a mask to form doped regions in the exposed portions of the substrate; removing the second mask layer; forming a field isolation layer on the substrate using the first mask layer as a mask, while the doped region under the field isolation layer between the first part and the at least one second part of the first mask layer serves as a drift region, and the doped region under the field isolation layer at the periphery of the at least one second part of the first mask layer serves as a modifying doped region; removing the first mask layer; forming a gate dielectric layer and a gate covering the channel region; and forming a source region and a drain region in the substrate beside the gate using the gate and the field isolation layer as a mask.
 2. The method of claim 1, wherein the first part of the first mask layer is apart from the two second parts of the first mask layer, and the opening in the second mask layer exposes the substrate between the first part and the two second parts of the first mask layer and exposes another portion of the substrate at the peripheries of the two second parts of the first mask layer.
 3. The method of claim 1, wherein the opening in the second mask layer exposes a portion of the substrate completely surrounding the at least one second part of the first mask layer.
 4. The method of claim 1, wherein the step of forming the field isolation layer comprises: performing a thermal oxidation process to form a field oxide (FOX) layer on the substrate using the first mask layer as a mask.
 5. The method of claim 1, wherein the step of forming the source region and the drain region comprises: forming two heavily doped contact regions in the substrate beside the gate using the gate and the field isolation layer as a mask; and forming two lightly doped grade regions in the substrate beside the gate using the gate and the field isolation layer as a mask, wherein the grade regions are formed deeper than the contact regions.
 6. The method of claim 1, wherein the step of implanting the dopant into the substrate is performed in a dosage ranging from 10¹²/cm² to 10¹⁴/cm².
 7. The method of claim 1, wherein the first mask layer comprises SIN.
 8. The method of claim 1, wherein the second mask layer comprises a patterned photoresist layer. 